Drum-typed brake is one of the important systems of vehicles and is a brake system applied in vehicles at the earliest time. Its greatest advantage lies in that it is simple in structure and economical in cost, but it can provide a potent braking force, and it can also be easily installed and maintained.
At present, integrally cast drum-typed brake is widely used in heavy trucks. The integrally cast drum-typed brake comprises a brake drum and a brake shoe. The brake shoe is mounted in the brake drum and can contact with the inner side face of the brake drum. The brake drum is mounted on the wheels and rotates with the wheels during moving of an automobile. When braking, the brake piston will push the brake shoe outwardly to make it press against the inner side face of the brake drum, and the frictional resistance between the shoe and the brake drum slows down or stops the moving automobile, so as to ensure driving safety.
When a vehicle is heavily loaded or moving in a high speed, especially when going down a long or steep slope, a large braking force and continuous multiple times of braking are required to ensure the controllable condition of the vehicle, which causes the temperature of the inner wall of the brake drum rise rapidly and the temperature difference between the interior and exterior of the brake drum increase, resulting in a sharp decreasing of the high temperature mechanical properties of the materials making up the brake drum and also a decrease of fatigue strength of the materials. The traditional material of brake drum is gray cast iron which has advantages of large friction coefficient and excellent heat transfer property, while its strength is low and brittleness is large. In order to reduce the negative effect brought by these features, the wall of the brake drum must be made very thick, so as to ensure a higher structural strength of the brake drum. A thick wall, however, will cause the temperature difference between the interior and exterior of the brake drum body to increase during braking, which in turn produces a large temperature difference stress and causes the high temperature mechanical properties of materials to deteriorate, and furthermore, because the resulting expansion stress cannot be eliminated in time, the brake drum body develops longitudinal micro cracks, which gradually develops into a lot of cracks and finally causes fracture. Thus, the service life of the integrally cast drum-typed brake is short.
A thickened brake drum wall will also increase the weight of the whole vehicle, increase gasoline consumption and manufacturing cost, which is not good for energy conservation and emission reduction.
Moreover, it is well known that brake drums will be in a high temperature state after braking, if it contacts with water, the drum body may be heat-cracked and blown out due to the chilling, and more seriously, the brake drum can burst and fly out causing safety accidents, and therefore, the safety of use is poor.
Various attempts have been made in improving the conventional drum brakes for increased strength, heat dissipation, and durability, and lightened weight. For example, composite brake drums were made that contain a steel shell with gray cast iron centrifugally cast into the steel shell. The steel shell provides the structural strength to prevent cracking, and the gray iron liner provides the wear surface for the brake lining and heat absorption from the friction of the brake lining. The composite brake drum is conventionally fortified by a “squealer band”, positioned near the inboard, open end of the brake drum, to provide rigidity and to prevent cracks that may start at the open end. An improvement of this configuration, U.S. Pat. Publication No. US2009/0065313, locates the squealer band midway along the width of the brake drum main body, to provide efficient use of the brake structure to receive the force from the brake shoe, and to absorb the most heat, because the mid-point of the brake drum is the portion on which the most force is exerted from the brake shoe.
These prior art brake drums still suffer from the above discussed drawbacks. For example, the steel shell is a poor heat conductor. Attempts were made to facilitate heat dissipation by adding axial fins or rigs to the squealer band, see e.g. US 2008/0308364, but the results remain unsatisfactory.